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Rapid and reversible shape changes of molecular crystals on photoirradiation

Abstract

The development of actuators based on materials that reversibly change shape and/or size in response to external stimuli has attracted interest for some time1. A particularly intriguing possibility is offered by light-responsive materials, which allow remote operation without the need for direct contact to the actuator. The photo-response of these materials is based on the photoisomerization of constituent molecules (typically trans–cis isomerization of azobenzene chromophores), which gives rise to molecular motions and thereby deforms the bulk material. This effect has been used to create light-deformable polymer films and gels2,3,4,5,6,7,8,9,10, but the response of these systems is relatively slow. Here we report that molecular crystals based on diarylethene chromophores and with sizes ranging from 10 to 100 micrometres exhibit rapid and reversible macroscopic changes in shape and size induced by ultraviolet and visible light. We find that on exposure to ultraviolet light, a single crystal of 1,2-bis(2-ethyl-5-phenyl-3-thienyl)perfluorocyclopentene changes from a square shape to a lozenge shape, whereas a rectangular single crystal of 1,2-bis(5-methyl-2-phenyl-4-thiazolyl)perfluorocyclopentene contracts by about 5–7 per cent. The deformed crystals are thermally stable, and switch back to their original state on irradiation with visible light. We find that our crystals respond in about 25 microseconds (that is, about five orders of magnitude faster than the response time of the azobenzene-based polymer systems7,8,9,10) and that they can move microscopic objects, making them promising materials for possible light-driven actuator applications.

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Figure 1: Chemical structures and deformation of the two diarylethene compounds.
Figure 2: Time dependence of the photo-response of single crystals of 1 and 2.
Figure 3: Reversible bending of a crystalline rod.
Figure 4: Molecular packing of a crystal of 1.

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Acknowledgements

The present work was supported by Grant-in-Aid for Scientific Research on Priority Areas and Nanotechnology Support Project from the Ministry of Education, Culture, Sports, Science and Technology, Japan.

Author Contributions M.I. designed the study, and wrote the paper. S.K. and T.I. performed experiments on compound 1. S.T. and H.M. performed experiments on compound 2.

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Correspondence to Masahiro Irie.

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Supplementary information

Supplementary Information

This file contains Supplementary Methods, Supplementary Tables S1 and S2, Supplementary Figures S1 – S8 with Legends and additional references. The file contains details of sample preparation, IR and UV-visible absorption spectra and X-ray crystallographic analysis data. Also included are the results of reversibility of the corner angle of single crystal 1 and response time measurement of deformation of rod-like crystal 2. (PDF 2519 kb)

Supplementary Movie 1

This file contains Supplementary Movie 1. The movie shows the reversible shape change of hexagonal crystal 1 (15 × 15 × 0.6 micrometer) upon irradiation with 365 nm and visible light (> 500 nm). To save the file size 3 min movie was shortened to 10 sec movie. (MOV 2857 kb)

Supplementary Movie 2

This file contains Supplementary Movie 2. The movie shows the reversible length change of rectangle crystal 2 (20 × 10 × 0.3 micrometer) upon irradiation with 365 nm and visible light (> 500 nm). To save the file size 30 sec movie was shortened to 10 sec movie). (MOV 3180 kb)

Supplementary Movie 3

This file contains Supplementary Movie 3. The movie shows the reversible bending of rod-like crystal 2 (30 × 2 × 2 micrometer) upon irradiation with 365 nm and visible light (> 500 nm). To save the file size 30 sec movie was shortened to 10 sec movie. (MOV 694 kb)

Supplementary Movie 4

This file contains Supplementary Movie 4. The movie shows a movement of a gold micro-particle by rod-like crystal 2 (250 × 5 × 5 micrometer) upon irradiation with 365 nm light. The speed of the movie is slowed down as much as 33 times. Real time of the movement is around 0.3 sec. (MOV 1843 kb)

Supplementary Movie 5

This file contains Supplementary Movie 5. The movie shows a shot of a silica micro-particle by rod-like crystal 2 (300 × 5 × 5 micrometer) upon irradiation with 365 nm light. The speed of the movie is slowed down as much as 100 times. Real time of the movement is around 0.1 sec. (MOV 821 kb)

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Kobatake, S., Takami, S., Muto, H. et al. Rapid and reversible shape changes of molecular crystals on photoirradiation. Nature 446, 778–781 (2007). https://doi.org/10.1038/nature05669

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